World tennis was rocked on Monday by allegations that the game's authorities have failed to deal with widespread match-fixing, just as the Australian Open, the first grand slam tournament of the year, kicked off in Melbourne.

Tennis authorities rejected reports by the BBC and online BuzzFeed News, which said 16 players who have been ranked in the top 50 had been repeatedly flagged to the Tennis Integrity Unit (TIU) over suspicions they had thrown matches in the past decade.

Eight of those players were taking part in the Australian Open, the BBC and BuzzFeed News said.

The media reports, which follow corruption scandals in world soccer and athletics, created a stir at the event at Melbourne Park, with players expressing surprise at the allegations.

"When I'm playing, I can only answer for me, I play very hard, and every player I play seems to play hard," women's world number one Serena Williams told reporters.

"If that's going on, I don't know about it."

Men's world number seven Kei Nishikori of Japan said he had not heard of any incidence of match-fixing.

The BBC and BuzzFeed News said the TIU, set up to police illegal activities in tennis, either failed to act upon information that identified suspicious behavior amongst players, or impose any sanctions.

All of the 16 players, including winners of Grand Slam titles, were allowed to continue competing, the media reports added.

TIU director of integrity Nigel Willerton told reporters in Melbourne he would not comment on whether any players on the pro tour were under investigation, saying it would be inappropriate to do so.

Reuters was unable to independently verify the findings by the BBC and BuzzFeed News, which said they had obtained documents that included the findings of an investigation set up in 2007 by the Association of Tennis Professionals (ATP), the governing body of men's professional tennis.

The BBC and BuzzFeed News said they had not named any players because without access to their phone, bank and computer records it was not possible to determine whether they took part in match-fixing.

"The Tennis Integrity Unit and the tennis authorities absolutely reject any suggestion that evidence of match fixing has been suppressed for any reason or isn't being thoroughly investigated," said ATP chairman Chris Kermode.

"While the BBC and BuzzFeed reports mainly refer to events from about 10 years ago, we will investigate any new information," Kermode told a hastily arranged media conference at Melbourne Park.

Betting syndicates

The media reports said the 2007 ATP inquiry found betting syndicates in Russia, northern Italy and Sicily making hundreds of thousands of pounds betting on games which investigators thought to be fixed.

Three of these games were at Wimbledon.

In a confidential report for tennis authorities in 2008, the inquiry team said 28 players involved in those games should be investigated but the findings were never followed up, the news organizations said.

Tennis authorities introduced a new anti-corruption code in 2009 but after taking legal advice were told previous corruption offences could not be pursued, they added.

Craig Tiley, Tennis Australia chief executive and Australian Open tournament director, said the Melbourne event had robust anti-corruption systems place.

"All involved in the administration of the Australian Open will not tolerate any deviations from our values and rules at any level," Tiley said.

Kermode added he was disappointed the story had taken attention away from the tournament.

"We are confident that the Tennis Integrity Unit is doing what it can and tackles this issue very, very seriously," Kermode said.

TIU investigations had resulted in sanctions against 18 players, with six issued life bans, he added.

Kermode also rejected suggestions the TIU was under-resourced and did not have necessary enforcement powers.

Tennis authorities have pumped about $14 million into anti-corruption programs, Kermode added.

TIU's Willerton said they could ask for players' electronic communication devices, though those requests could be refused.

"If they don't then consent ... that's called non-cooperation, and they can be reported and sanctioned for non-cooperation," Willerton said.

Independent Australian Senator Nick Xenophon said sports regulators were not rigorous enough and that the very nature of tennis made it possible to engage in spot fixing, where single events are manipulated to affect live betting odds.